Electronic commutator



p 1941- o. T. FRANCIS ELECTRONIC COMMUTATOR Filed June 29, 1939 2 Sheets-Sheet l Jrwowtoo Se t. 2, 1941. o. "r. FRANCIS 2,254,279

' ELECTRONIC COMMUTATOR Filed Juhe 29, 1939 2 sneets-s'heetz munication relatively free Patented Sept. 2,

UNITED STATE PATENT .OFFICE ELECTRONIC COMMUTATOR Oliver T. Francis, Renville, Minn. I Application June 29, 1939, Serial No. 281,965

18 Claims.

of rotating a cathode ray so that it will strike a plurality of anode targets in a predetermined sequence. Such systemsrequire extensive phasing and deflecting apparatus, necessitate the use of highflvoltages and require amplifying circuits for each of said targets before applied signals are strong enough to be utilized. 1

3. Thermionic'tube commutators, consisting of complicated circuits, whereby signals from one channel render the other channels inoperative. Such circuits are unstable. The number of tubes required for the performance of commutation increases in such circuits as the square of the number of channels.

None of these methods are suited for radio net transmission whereby a single station m'ay transmit to any one of a plurality of geographically separated stations, each of said plurality operating on a difierent channel due to the complexity and lack of flexibility of said methods.

It is an object of this invention to illustrate a method of multiplexing which shall include a minimum of equipment, which shall be free from the objectionable features of existing systems as outlined above.

Another object is to illustrate'a method of communication whereby a single synchronizing transmitting station may be utilized to maintain synchronism between any transmitting and receiving stations.

Another object is to illustrate a method whereby a carrier frequency may be multiplexed to carry a plurality of voice and telegraph signals. Another object is to illustrate a method of comturbances which shall consist of scanning a plurality of receiving units in synchronism with said transmitting units, of producing a current of said frequency. in each-of said receiving units corresponding to currents of said frequency flowing in said transmitting units, of selectively amplifying said current of said frequency in" said from atmospheric disdesired number L of neling by multiplex, and means receiving units and of translating said amplified current into signals. I

In U. S. Patent No. 1,819,599,'issued to me August 18, 1931, I illustrated a method of differentially applying a voltage to two grids in 'a vacuum tube in the path of anelectron stream, thereby rendering said tube conductive to only one predetermined magnitude of said voltage.

It is an object of this invention to illustrate means whereby the basic principles of said patent may be utilized for scanning a plurality of transmitting and receiving units in synchronism, and of controlling the conductivity of said transmitting and receiving units in accordance with a signal voltage impressed on a third electrode in said electron stream.

Another object is to illustrate a tube having a plurality of grids, means for differentially applying a voltage to twoof said grids to render said tube conductive only when said voltage reaches a predetermined value andmeans for controlling the conductivity of said tube when said voltage reaches said predetermined value in accordance with a signal voltage impressed on a third grid in the path of said electron stream.

Another object is to illustrate a vacuum tube commutator which shall be substantially free from the efiects of mechanical and electrical inertia, and capable of performing electrical commutation at any desired speed.

Another object is to provide a commutator wherein the lengths of time to which the units of said commutator responds may be of equal or unequal time length and easily changed from one time length to a longer or shorter period.

Another object is to illustrate a receiver unit in a time division signal system which shall respond to signals only during a period of time when a corresponding transmitting unit may transmit and means for readily amusting the length of said period at said transmitting and said receiving station. A

r Another object is to illustrate a. selective system,-any one of a plurality of electro-responsive devices at a receiving station being operable upon the operation of a corresponding unit at a transmitting station.

Another object is to provide a. plurality of channels by multiplexing, and means for further multiplexing each of said channels.

Another object is to provide means for chanfor further channeling each' of the first channels at a slower speed than said first channels are channeled.

Another object is to provide a negative channel information system, such as for fire alarms which are operated only in case of a fire.

With these and other objects in view, the invention may be more readily understood by reference to the following description taken in connection with the drawings in which:

Fig. 1 is a transmitting station for sending out synchronizing pulses.

Fig. 2 is a multiplex transmitting station.

Fig. 3 is a receiving station for multiplex signals.

Fig. 4 is another receiving station geographically remote from the station shown in Fig. 3.

Fig. 5 is a synchronizing station similar to Fig. 1.

Fig. 6 is another synchronizing station operating on a frequency different than Fig. 5.

Fig. 7 is a multiplex transmitting station and,

Fig. 8 is a multiplex receiving station for receiving signals sent out by Fig. '7.

The synchronizing station shown in Fig. 1 comprises conventional type of tuned plate tuned grid circuit, consisting of vacuum tube VI, B battery BI, condenser CI, in parallel with inductance LI, feedingantenna ANI, grid condenser C2, grid inductance L2, biasing battery CBI, radio frequency by-pass condenser C3, A battery Al, The output of the transmitter is modulated by a synchronizing pulse generator comprising a neon oscillator NI, supplied with current from battery B2, a variable resistance RI in parallel with a condenser 04.

The synchronizing pulses from Fig. 1 are picked up at transmitting station Fig. 2 by antenna circuit tuned to 8000 kc. amplified through radio frequency amplifier RFC, and break down three electrode gas discharge device N2. Battery B3 charges condenser C5. The electronic .commutator at the transmitting station Fig. 2

comprises vacuum tubes V2, V3, V4, each having an anode, a cathode, and three grids. These grids have been designated as GI, G2, G3, G4, G5, G6, G1, G8, G9, respectively. The grids closest the anodes in these tubes GI,\G4, G7 are signal control electrodes. Grid G4 is normally biased past the current cut off by means of CB5.

Key KI. shorts resistance R6 and CB5, thereby allowing G4 to assume a zero potential. G1 is similarly biased past the current cut oil by CB4. Key K2 shorts CB4 and resistance R! to permit G1 to attain a zero potential and pass current when K2 is closed. The signal grid GI of V2 is controlled by Voltage variations across R8, in accordance with voltage variations produced by microphone MI as amplified by vacuum tube V5. CB8 has been placed in the grid circuit of GI to place the proper operating voltage thereon.

The commutator or scanning grids G2, G3, G5, G5, G8, G9, have been differentially connected through biasing batteries CB2, CB3, in a manner similar to that described in U. S. Patent No. 1,819,599, so that the potential drop across R2, R3 is differentially applied, thereby rendering each of vacuum tubes V2, V3, V4 conductive to one predetermined voltage across R2, R3. Resistances R9, RIB, RII, RIZ, RI3, RI4 are all high resistances to prevent G2, G3, G5, G6, G8, G9 from assuming a positive potential as the voltages across R2, R3 is varied. In the plate circuit of V2, V3, V4 is B battery B4, and resistance RI5. The vacuum tube transmitter V6 is of the conventional tuned plate tuned grid circuit being normally biased to the out off point by C batpasses through RI5, in response to current through commutator tubes V2, V3, V4. B5 has een connected in the plate circuit of V3 as a means of varying the time V3 is conductive.

At the receiving station Fig. 3, antenna 8000KC picks up synchronized pulse from Fig. 1, which is amplified through RFC and synchronizes the break down of gas discharge device N3 with N2 at the transmitting station Fig. 2 charging condenser C6 in parallel with resistances RIG, RI'I. Commutator tubes V8 and VI 0 are similar to tubes V2 and V3 at the transmitting station, having signal grids GIO and GI3. The commutation grids GII, GI2, GI4, GI5 are similarly connected to biasing batteries CBIII, CBI I, so as to render V8 and VIII conductive in synchronism with their corresponding commutator units at the transmitting station V2, V3. Resistances RI9, R20, R2I, R22 prevent these grids from assuming a large positive potentialas the voltage across C6 is varied.

The signal grid GIII of V8 is controlled by the voltage drop across RI8, in accordance with the signal picked up by antenna 10,000KC, amplified by radio frequency amplifier RFC, C-bias detector V1,-in the output circuit of which is plate battery B8 and radio frequency bypass condenser 01. Biasing battery CBI 5 places the proper voltage upon GIO. In the output circuit of V8 is connected anode battery B1 and transformer primary L2. Transformer secondary inductance L3 is connected in parallel with variable condenser (38, so as to be tuned to the synchronizing frequency of N I, which in the present instance may be 20,000 cycles per second. C-bias amplifier detector V9, with C battery CBIB, anode battery B9 and electro-responsive device H as plate load is connected so as to amplify current passing through V8 which corresponds to current flowing through commutator unit V2.

Grid GI3 of commutator unit VIO which corresponds to unit V3, at the transmitting station is connected through biasing battery CBII across RIB. In the anode circuit of VI 0 is battery B1 and transformer primary inductance L4. The voltage source B1 is made variable in order that the length of time to which VI 0 is conductive may be made variable in accordance with the length of time V3 is rendered conductive by varying B5. Transformer secondary inductance L5 in parallel with variable condenser C9 is tuned to the synchronizing frequency of NI, which voltage is amplified by C-bias detector VII, in the grid circuit of which is biasing battery CB I44, and in the output circuit of which is battery BID and signal recorder REC, which may be of any known construction or a synchronizing recorder system such as illustrated in Fig. 8.

Outlying station Fig. 4 is similar to Fig. 3 and is shown merely to illustrate the flexibility of my system of commutation, which renders it applicable for net operation, which is not practicable for existing methods of multiplex. It consists of antenna circuit 8000KC, radio fre quency amplifier RFC, gas discharge device N4, and BI I, which produces synchronizing voltage across C20 in parallel with resistances R21, R20; commutator unit V20, with synchronizing grids G2I, G22, connected through R25, R26, biasing batteries CB20 and CB2I respectively. CB20 and CB2I have been chosen of such value that V20 is conductive only during the time its correspondtery CB9, but sending out signals as current ing commutator unit V4 at the transmitting station is conductive. The signal control grid G20 of V20 is supplied with a signal voltage from antenna- |0,000KC amplified through radio frequency amplifier RFC and detected by radio frequency detector DET. If then the synchronizing voltage from NI is made within the audible range by varying R], a signal may be heard of synchronizing frequency in electro-responsive device H2, when K2 is closed at the transmitting station.

From a consideration of the principles outlined in U. S. Patent No. 1,819,599 above referred to, it is evident that the commutator units V2, V3, V4 of Fig. 2 are each conductive at one predetermined voltage existing across C5. When N2 breaks down and charges C5 to a high potential, the voltage drop across R3 is sufliclent to cancel the efiect of the high negative voltage impressed upon G9. The voltage drop across R2 tends to impress a negative potential upon G which just cancels the positive potential impressed thereon by CB2. Therefore V4 becomes conductive. Neither V2 or V3 are conductive at this time since the voltage drop across R2 biases G2 and G5 past the current cut off.

As C5 discharges through R2, R3 the voltage drop across R3 becomes just suificient to cancel the negative potential impressed on G6 -by CB3, and the drop across R2 offsets the positive potential impressed upon G5 by CB2. V3 then becomes conductive. Neither V2 or V4 are conductive at this time since CB3 lbiases G9 past the current cut off of V4, and the voltage drop across R2 biases G2 past the current cut oil of V2.

Similarly, when C5 has discharged further CB3 biases V3 and V4 past the current cut ofi but G2 and G3assume zero potential and allow V2 to become conductive.

discharged to a predetermined magnitude of voltage. In the output circuit of V is anode battery B34 and load resistance R42 which controls radio transmitter operating on 10,000 kc. The frequencies of transmitters and synchronizing pulses are for illustration only and may of course be varied to meet the requirements.

The control grid G32 of V30 is biased past the current cut ofi by C3 and is prevented from ever assuming a high positive voltage by resistance R. The keying of G32 is efiected by a commutator system comprising V3l, V32.

The synchronizing pulses of 20 cycles per second sent out by Fig. 6 are picked up by antenna AN2 amplified by RFC and break down gas discharge device Nl, permitting B36 to charge condenser C3 l. The grids G33, G34 of V3l and G31, G30 of V32 havebeen connected through resistances R44, R60, R46, R48, CB36, CB31 in accordance with the manner previously described for the commutator tubes of Fig. 2, so as to render V31, V32 conductive when C3l has discharged "While I have illustrated but three commutator I units V2, V3, V4, it is evident that the number is limited only by the accuracy of the synchronizing means. It is not desired to limit my synchronizing means to that illustrated but any synchronizing method utilized in television art for scanning may be used. In=this connection it is noted that television screens normally comprise hundreds of thousands of elemental areas,

and as such elemental areas in the television screen corresponds to commutator units of Fig. 3, the number of channels possible in my system of multiplex is very large.

In Fig. 7, I have illustrated a means whereby each of the channels'shown in Fig. 2 may be further multiplexed, thereby making it possible to use each of the channels of Fig. 2 for teletype or for further additional multiplexed channels.

Referring to Fig. 5, a synchronizing transmitting station is shown. Fig. 5 is composed of transmitter TRAN operating on frequency of 8000 kc., and modulated by M to send out 1000 synchronizing pulses per second. Fig. 6 comprises a transmitter TRAN operating on 6000 kc., and sending out 20 synchronizing pulses per second.

Signal transmitting station Fig. 6, shows gas discharge device N6, which breaks down 1000 times per second in accordance with the synchronizing pulses received from Fig. '5 amplified by RFC. B30 charges C30 in parallel with resistances R30; R1. Vacuum tube V30 corresponding to vacuum tube V3 of Fig. 2 has its commutator grids G30 and G3l connected across R30, R31 through resistances R4l, R43 and biasing batteries CB30, CB3I, respectively, so as to render commutator tube V30 conductive when C30 has to a predetermined magnitude of voltage. The signal grid G35 is normally biased by C340 through R45 past the current cut off. When key D, which may be a circuit closed when the letter I D is impressed on a teletype machine, removes the negative bias on G35 and allows V3lto become conductive during the portion of the discharge cycle of C3l allotted to V3l. Similarly control grid G36 of V32 is normally biased by CB45 through resistance R41 past the current cut off. When key B is closed V32 is similarly rendered .conductive. In the output circuit of V31, V32 is connected resistance R38, which controls V30 and permits radio transmitter to send out 1000 cycle pulses as modulated by the 20 cycle pulses of V3l, V32. 7

The receiving station Fig. 8, comprises an antenna AN3 for picking up the 1000 cycle synchronizing pulses from Fig. 5, an amplifier for these pulses RFC to control the breakdown of gas discharge device N8 permitting battery B3! to charge condenser C32. Vacuum tube commutator unit V34 corresponds to V10 of Fig. 3, comprises a plurality of synchronizing grids G30, G40, connected through R50, R5l, CB32, CB33 respectively across R32, R33, so that it will pass current only'during the period of time that V30 at the transmitting station is conductive. The control electrode G41 of V34 is normally biased past the current cut oil by CB43. When a signal from transmitter station Fig. 7 is picked up by AN4, amplified and detected by C-bias detector V31 a positive voltage is impressed across R52 in parallel with C40, which permits V34 to pass current during the period of time that G39 and G40 are at zero potential with respect to the filament.

The recording system comprising antenna AN 5 for picking up the 20 cycle synchronizing pulse from Fig. 6, amplifier RFC, gas discharge device N9, which permits B31 to charge condenser C33. Vacuum tube commutator units V35, V36 with synchronizing grids G42, G43, G45, G46 are connected through R53, R54, R55, R56, to proper point on biasing batteries C334, C335, so that the voltage drop across R34, R35 will render V35, V36 conductive in synchronism with V3l, V32 at the transmitting station. The control grids G52, G44 are connected in parallel. Biasing battery CB44 normally-biases these tubes past the current cut ofi through resistance R51. When however plate current fiows in the output circuit of V34 from battery B32 through load resistance R60, the control grids G52, G44 assume a positive potential, and current flows in the output circuit from B30 through selector magnet D or B when the keys D or B at the transmitting station Fig. 7 are closed.

I have chosen synchronizing stationsFig. -5, Fig. 6 to operate on frequencies different than transmitting station Fig. 7. I am cognizant of the fact that synchronism has been obtained in multiplex system utilizing one of the commutator channels to maintain synchronism. The use of synchronizing transmitters operating on different carriers is believed justifiable in view of the fact that it is contemplated to utilize a large number of signal stations for one carrier, and to utilize the synchronizing pulses for a number of stations operating on different carriers.

As indicated above the number of stations, which it is possible to place on a single carrier is limited only by the accuracy of the synchronizing means. The magnitude of the voltage to which a gas discharge device will charge a condenser, varies somewhat with temperature, the proximity to radio active substances, light; etc. Known methods of magnitude voltage control may be utilized to stabilize this variation, one form of which is shown in Fig. 8, where three element vacuum tube V90, has been placed in parallel with condenser C32. As is well known tubes connected as V90 are highly conductive'to currents when the anode voltage impressed thereon exceeds a predetermined value, depending upon the value of the biasing battery C390, but have a very high resistance to anode voltages below that value. If N8 charges C32 to a higher voltage than said predetermined value, C32 is rapidly discharged to said value, thereby permitting V34 to be operated in synchronism with corresponding transmitting station unit, regardless of variations in the magnitude to which N8 charges C32.

In Fig. 1, I have shown a synchronizing pulse transmitter wherein the frequency of the pulses produced may be varied by variable resistance RI. For the purpose of illustrating the operation of the voice transmission and receiving means comprising V2 and V8 of Figs. 2 and 3, respectively I have assumed in the above specification, this synchronizing frequency to be a supersonic frequency of 20,000 cycles per second. The voice currents from MI impressed on GI of V2 modulate the 20,000 cycle pulses, and these modulated pulses in turn modulate the radio frequency waves being transmitted by V6. These double modulated waves are picked up by antenna and RFC circuits associated with V! and applied to Gl of V8. They are then amplified by the C-bias detector circuit comprising the tube V9 which is connected to the tuned circuit including the secondary of transformer L3, and the condenser C8, tuned to 20,000 cycles per second. This amplification at the synchronizing frequency of 20,000 cycles per second is similar to intermediate frequency amplification so effectively used in amplifier circuits today, whereby the voice frequencies which are superimposedon the intermediate frequency are amplified.

For operation of the syphon recorder, comprising circuits incorporating V3 and VIII, this synchronizing frequency has been again assumed to be 20,000 cycles per second. Secondary of 1 L and C9 have been tuned to 20,000'cycles for amplification of the synchronizing frequency.

For the operation of the channel incorporating tubes V4 and V20 this synchronizing frequency has been changed to an audible frequency, such as 500 cycles per second, by varying resistance RI, in order to render the signal audible in headphones H2. As previously indicated channel comprising V4-V20 was illustrated merely to show that the system is adaptable to transmission of the International code. Obviously the other two channels comprising V2-V8 and V3-VIO, which as previously indicated are tuned to 20,000 cycles per second would be inoperative when channel V4-V20 was operating on 500 cycles, unless these channels were returned to that frequency.

Synchronizing'pulse transmitters Fig. 5 and Fig. 6 have been illustrated as sending out pulses of 1000 and 20 cycles per second, respectively. As indicated previously in this specification these transmitters are similar to the one shown in Fig. 1. While 1000 cycles is harmonically related to 20, it is obvious that with separate transmitters of the type shown in Fig. 1, that it would be impossible for the synchronizing frequencies to be controlled so accurately as to maintain a harmonic relation between them and it is not intended to limit their operation to harmonic relationship, all synchronizing frequencies having been chosen for illustration of the operation of the circuit. The advantage of using a plurality of non-interdependent synchronizing voltages is that variations in the frequency of one of said voltages are compensated for by the other. Noninterdependent synchronizing voltages as used in this specification and appended claims, are defined as synchronizing voltages wherein changes in frequencies of one of said voltages due to apparatus imperfections produce no change in the frequency of a second of said synchronizing voltages.

While my electronic commutator has been illustrated in connection with multiplex channeling of carrier frequencies, it is apparent that it may be used in many other ways where high speed commutation is desired without departing from the spirit of the invention. Use in selector systems at once suggest itself, especially in the field of automatic telephony. It is not desired to limit the invention to the forms described above. The invention is to be limited only by prior art and as described in the following claims:

What is claimed is:

1. In a multiplex communication system, a plurality of electronic commutators, each of said commutators comprising a plurality of vacuum tube commutator units, each of said vacuum tubes having a. plurality of grids, means for maintaining synchronism between said commutatcrs, said means comprising means for producing a synchronizing voltage, means for applying said voltage to two of the grids in each of said tubes, to tend to produce a positive potential on one of said two grids of each of said vacuum tubes and a negative potential on a second of said two grids of each of said tubes, means for biasing the grids of corresponding units of said commutators to render said corresponding units conductive simultaneously.

2. An electronic commutator, comprising: a plurality of unit vacuum tubes, each of said vacuum tubes having a plurality of grids, means for generating a varying voltage, means for rendering each of said tubes conductive at difierent magnitudes of said voltage, said last means comprising means for applying said voltage to said grids to tend to produce a positive potential on one of said grids of each of said tubes, and a negative potential on a'second of said grids of .late the electronic current flow of each of said depending on the conductive anode to cathode voltage drop of said device.

4. A multiplex system, comprising: a transmitting station, a receiving statio an electronic commutator comprising units cyclically operable in succession at different magnitudes of a varying voltage at each of said stations, means at each of said stations for generating a voltage of predetermined magnitude for starting said succession, said means comprising a source of potential, a resistance and a condenser, and a gas discharge device, said device having an anode and a cathode, the conductive anode to cathode potential drop of said device being substantially independent of current flow, and means for rendering said gas discharge device at each of said stations conductive simultaneously.

5. A.multiplex system, comprising: a transmitting station, a receiving station, an electronic commutator at each of said stations, said electronic commutator comprising a, plurality of unit vacuum tubes, each having a plurality of grids, means for simultaneously producing a voltage of predetermined magnitude at each of said stations, means for applying said voltage to said grids of said vacuum tubes at each of said stations to tend to produce a positive potential on one of said grids and.a negative potential on a second of said grids, means for preventing any of said grids from, assuming an excessive positive potential, said last means comprising a separate high resistance in series with each of said grids, means for biasingsaid grids of said unit vacuum tubes in diflerent magnitudes to render said tubes conductive-at different magnitudes of said voltage, and means for varying the magnitude of said voltage produced at each of said stations to render said unit vacuum tubes sequentially operable in synchronism.

6. The method of transmitting signals in multiplex communication with a plurality of groups of channels, which consists in cyclically rendering a first group of said channels operable at a predetermined frequency, controlling a first group of said channels by a second group of channels cyclically operable at a difierent frequency, controlling said second channels by said signals, and selectively amplifying said signals at said first mentioned frequency.

7. An electronic commutator adapted for multiplex signaling systems and the like, comprising: electronic discharge device means having a plurality of electron current paths,v each of said paths having a cathode, an anode and a plurality ofcontrol electrodes for controlling the electronic current flow between said cathode and anode, means for applying a varying control potential to selected ones of said control electrodes of each of said paths periodically to periodically vary the sensitivity of each of said electronic commutator paths, the sensitivity of different ones of said paths being maximum for difierent values of said varying potential, and means for applying signaling energy to another of said control electrodes in each of said paths to moduelectronic commutator paths.

8. A multiplex signaling system electronic commutator, comprising: a condenser, means for periodically charging said condenser, a discharge circuit connected to said condenser, a multiple 'grid vacuum tube having a pair of the grids thereof diiferentially connected to said discharge circuit so that one of said grids is at a positive potential with respect to the cathode of said vacuum tube while the other of said grids is at a negative potential, means for biasing said grids to maintain said vacuum tube substantially nonconductive except when the effects of the potentials on said pair of grids neutralize to permit useful current flow through said vacuum tube,

and means for modulating the useful current flowing through said vacuum tube.

9. A multiplex signaling system electronic commutator, comprising: a condenser, means for periodically charging said condenser, a discharge circuit connected to said condenser, a vacuum tube having a cathode, an anode and a plurality of grids, means for differentially connecting a pair of said grids to said discharge circuit so that one of said pair of grids is charged positively with respect to the cathode of said vacuum tube while the other of said pair of grids is charged negatively, means for biasing said pair of grids to permit useful current to flow substantially only when said positive charge neutralizes said negative charge, and means for impressing signal energy on another of said grids to control the useful current flow in said vacuum tube.

10. A multiplex signaling system electronic commutator, comprising: a condenser, means for periodically charging said condenser, a discharge circuit connected to said condenser, a plurality of multiple grid vacuum tubes each having a pair of the grids thereof differentially connected to said discharge circuit to control the useful current flow through each of said tubes, means connected to said discharge circuit and to said pairs of grids of said vacuum tubes to render said vacuum tubes conductive in sequence as said condenser discharges through said discharge circult, and means for signal modulating said ourrent flowing through each of said tubes.

11. A multiplex signaling system electronic commutator, comprising: a condenser, means for periodically charging said condenser, a discharge circuit connected to said condenser, a plurality of multiple gridvacuum tubes each having a pair of the grids thereof differentially connected to said discharge circuit so that one of said pair of grids is at a positive potential with respect to the cathode of the corresponding vacuum tube while the other of said pair of grids is at a negative potential to permit useful current to flow through each of said vacuum tubes substantially only when the effects of said potentials on said pairs of grids substantially neutralize, means connected to said discharge circuit and to said pairs of grids of said vacuum tubes to render said vacuum tubes conductive in sequence as said condenser discharges through said discharge circuit, and means for impressing a signal on said current flowing through each of said vacuum tubes.

12. A multiplex signaling system electronic commutator, comprising: a condenser, means for periodically charging said condenser, a discharge circuit connected to said condenser, a multiple gridvacuum tube having a pair of the grids thereof differentially connected to said discharge circuit to permit useful current to flow through said vacuum tube only when the potentials impressed on said difierentially connected grids substantially counteract each other to permit an electron current to flow from the cathode to the anode of said vacuum tube, and means for impressing signaling energy on another or said grids to control the current flow through said vacuum tube. i

13. In an electrical system, means for generating electrical pulses at desired time intervals, means for producing a voltage, a vacuum tube having a plurality of grids, means for applying said voltage to two grids in said vacuum tube, to tend to produce a positive potential on one of said grids, and a negative potential on a second of said grids, and means for biasing said grids to render said vacuum tube conductive at a desired portion of said time intervals.

14. In a time division system, means for gen-- erating electrical voltages at predetermined time intervals, an electronic commutator, comprising a plurality of vacuum tubes each having a plurality of grids, means for applying said voltages to two of said grids in each of said vacuum tubes, to tend to produce a positive potential on a first of said grids of each of said vacuum tubes and a negative potential on a second of said grids of each of said vacuum tubes, and means for biasing the grids of each of said vacuum tubes in different magnitude, to render each of said vacuum tubes conductive at different portions of said time intervals.

-15L An electronic commutator, comprising: a plurality of unit vacuum tubes, each of said vacuum tubes having a plurality of grids, means for generating a varying voltage, means for rendering each of said tubes conductive at different magnitudes of said voltage, said last means comprising means for applying said voltage to said grids to tend to produce a positive potential on one of said grids of each of said tubes, and a negative potential on a second of said grids of each of said tubes.

16. The combination with a plurality of electronic commutators, each of said commutators comprising a plurality of commutator unit vacuum tubes, each of said vacuum tubes having a plurality of grids, means for maintaining synchronism between said commutators, said means comprising means for producing a synchronizing voltage, means for applying said voltage to two of the grids in each of said tubes, to tend to produce a positive potential on one of said two grids of each of said vacuum tubes and a negative potential on the other of said two grids of each of said vacuum tubes, and means for biasing the grids of corresponding units of said commutator to render said corresponding units conductive simultaneously.

17. A commutating device comprising: an electronic commutator, comprising a plurality of vacuum tubes, each of said vacuum tubes having a plurality of grids, means for generating a varying voltage, means for rendering each 01' said vacuum tubes conductive at difierent magnitudes of said voltage, said last means comprising means for applying said voltage to said grids to tend to produce a positive potential on one of said grids of each of said tubes, and a negative potential on a second of said grids of each of said vacuum tubes, means for impressing signal energy on a third of said grids in one of said tubes, said last mentioned means comprising a second electronic commutator comprising a plurality of unit vacuum tubes, each having a plurality of grids, means for generating a second varying voltage, means for rendering each of said tubes or said second commutator conductive at difierent magnitudes of said second voltage, said last means comprisingmeans for applying said second voltage to said grids of said tubes of said second commutator to tend to-produce a positive potential on one of said grids and a negative potential on a second of said grids of said vacuum tubes of said second commutator, meansfor impressing signal energy on a third of said grids of each oi. said vacuum tubes of said second conmiutator, and means for impressing signal energy produced by said second commutator on said third grid of said one of said vacuum tubes of said first commutator.

18. A eommutating device comprising: an electronic commutator comprising a plurality of unit vacuum tubes each of said vacuum tubes having a plurality of grids, means for generating a varying voltage, means for rendering each of said tubes conductive at different magnitudes of said voltage, said last means comprising means for applying said voltage to said grids to tend to produce a positive potential on one of said grids of each of said tubes and a negative potential on a second of said grids of each of said tubes, means for impressing signal energy on a third of said grids in each of said tubes, a second electronic commutator comprising a plurality of unit thermionic tubes each having a plurality of control electrodes, means for generating a second varying voltage, means for rendering each of said thermionic tubes conductive at difierent magnitudes of said second voltage, said last mentioned means comprising means for applying said second voltage to said control electrodes to tend to produce a positive potential on one of said control electrodes of each of said thermionic tubes, and a negative potential on a second of said control electrodes of each of said thermionic tubes, and means for impressing signal energy generated by one of said unit vacuum tubes on a third or said control electrodes in each of said thermionic tubes.

OLIVER T. FRANCIS. 

